LED driving circuit reaches the circuit in order to the power controlling switch
Technical field
The present invention relates to a kind of light-emitting diode (Light Emitting Diode) drive circuit, and be particularly related to a kind of circuit, it utilizes pulse-width modulation (Pulse Width Modulation is called for short PWM) to use the power switch of control LED driving circuit.
Background technology
Fig. 1 is the schematic diagram of known a kind of LED driving circuit 100.LED driving circuit 100 is made of booster type DC-DC transducer 130 and load 120 thereof.Load 120 comprises the light-emitting diode 104 and a current mirror 103 of a plurality of serial arrangement, and wherein current mirror 103 couples the light-emitting diode 104 of serial arrangement.Boosting type converter 130 comprises inductance L 1, switch Q1, PDM keyer 101, diode D1, resistance R 11, R12 and capacitor C 1.First termination of inductance L 1 is received input voltage vin 1, and its second end couples first end of switch Q1.The anode of diode D1 couples first end of switch Q1, first end of the negative electrode coupling capacitance C1 of diode D1.Second termination of capacitor C 1 is received earthed voltage.PDM keyer 101 is utilized pulse-width signal PS1, uses control switch Q1.When switch Q1 conducting, the electric current of the inductance L of flowing through 1 then can increase.When switch Q1 closed, the energy that inductance L 1 is accumulated then can be transferred to capacitor C 1, used and kept the driving voltage Vout1 that offers light-emitting diode 104.Resistance R 11, R12 constitute a bleeder circuit, in order to provide feedback voltage FB1 to PDM keyer 101.101 work periods (Duty Cycle) of PDM keyer according to feedback voltage FB1 decision pulse-width signal PS1.
The glow color of light-emitting diode is determined by drive current.The brightness of light-emitting diode was controlled by the work period of its drive current.For instance, when the work period of drive current was 50%, brightness then was 50% of maximum level.In LED driving circuit 100, when dimming control signal DCS1 enables, 103 of current mirrors provide the drive current of the light-emitting diode 104 of flowing through, and when dimming control signal DCS1 is forbidden, 103 drive currents of current mirror by the light-emitting diode 104 of flowing through.Therefore, the work period of dimming control signal DCS1 is the work period of light-emitting diode 104 drive currents.
Switch Q1 is power metal-oxide-semiconductor field effect transistor (Power Metal OxideSemiconductor Field Effect Transistor is called for short Power MOSFET).Power metal-oxide-semiconductor field effect transistor is the large-sized external element.Whenever by the gate terminal conducting or when closing power metal-oxide-semiconductor field effect transistor, can consume sizable power.And PDM keyer 101 is understood output pulse width modulation signal PS1 constantly.In other words, even dimming control signal DCS1 forbidding, power switch Q1 still can carry out switch motion, therefore causes the low and waste power of usefulness.Along with the work period of dimming control signal DCS1 is lower, this problem then can heal and become serious.In addition, unnecessary switch motion not only can overcharge (Overcharge) to capacitor C 1, but also can enlarge the ripple (Ripple) of driving voltage Vout1.
Summary of the invention
The invention provides a kind of LED driving circuit and in order to the circuit of power switch of control LED driving circuit.When the drive current of light-emitting diode ends, above-mentioned circuit is then closed power switch and is used and prevent unnecessary switch motion.Therefore, above-mentioned circuit can reduce power consumption and raise the efficiency.In addition, another characteristics of above-mentioned circuit are, can not overcharge to electric capacity, so the ripple of driving voltage then can diminish.
The present invention proposes a kind of LED driving circuit, comprises switch, PDM keyer, current source and signal controller.The first end outputting drive voltage of switch is given light-emitting diode.PDM keyer provides pulse-width signal.When dimming control signal was enabled, current source then provided the drive current light-emitting diode of flowing through.When dimming control signal was forbidden, signal controller is off switch then, and when dimming control signal was enabled, signal controller then was passed to switch with the pulse-width signal of PDM keyer, uses control switch.
In one embodiment of this invention, LED driving circuit also comprises buffer, is coupled between signal controller and the switch.
In one embodiment of this invention, LED driving circuit also comprises voltage detector, in order to produce feedback signal, this feedback signal is in order to the state of indication driving voltage, and PDM keyer is according to the work period of feedback signal decision pulse-width modulation control signal.
In one embodiment of this invention, when this feedback signal was indicated the error condition of driving voltage, PDM keyer was then enabled rub-out signal.When driving voltage was lower than a threshold value, state then made a mistake.When rub-out signal was enabled, even dimming control signal forbidding, the pulse-width signal that signal controller will PDM keyer was passed to switch.
In one embodiment of this invention, signal controller comprises or door and and door.Or door is in order to receive dimming control signal and rub-out signal.With door in order to receive pulse-width signal with or the output signal of door.Wherein with the output signal of door in order to control switch.
From another viewpoint, the present invention proposes a kind of circuit, in order to the power controlling switch, in order to provide driving voltage to light-emitting diode, wherein when dimming control signal is enabled, then provides the drive current light-emitting diode of flowing through.This circuit comprises PDM keyer and signal controller.PDM keyer is in order to provide pulse-width signal.When dimming control signal was forbidden, signal controller was closed power switch, and when dimming control signal was enabled, signal controller then was passed to power switch with the pulse-width signal of PDM keyer, used the power controlling switch.
For above-mentioned feature and advantage of the present invention can be become apparent, preferred embodiment cited below particularly, and conjunction with figs. are described in detail below.
Description of drawings
Fig. 1 is the schematic diagram of known a kind of LED driving circuit 100.
Fig. 2 is the schematic diagram of a kind of LED driving circuit 200 of one embodiment of the invention.
Fig. 3 is the schematic diagram of a kind of LED driving circuit 300 of another embodiment of the present invention.
Fig. 4 is the schematic diagram of circuit of a kind of signal controller 302 of one embodiment of the invention.
Fig. 5 is the sequential chart of the signal of interest in the LED driving circuit 300.
[main element symbol description]
100,200,300: LED driving circuit
210,310: control circuit
120,220,320: load
130,230,330: booster type DC-DC transducer
101,201,301: PDM keyer
202,302: signal controller
103,203,303: current mirror
104,204,304: the light-emitting diode of serial arrangement
401: or door
402: with door
Q1, Q2, Q3, SW2, SW3: switch
D1, D2, D3: diode
C1, C2, C3: electric capacity
L1, L2, L3: inductance
R11, R12, R21, R22, R31, R32: resistance
FB1, FB2, FB3: feedback voltage
PS1, PS2, PS3: pulse-width signal
FS: rub-out signal
DCS1, DSC2, DSC3: dimming control signal
Vin1, Vin2, Vin3: input voltage
Vout1, Vout2, Vout3: driving voltage
SDS: output signal
T1~T6: time point
Embodiment
Fig. 2 is the schematic diagram of a kind of LED driving circuit 200 of one embodiment of the invention.LED driving circuit 200 is the improvement of known luminescence diode drive circuit 100.Briefly, when switch SW 2 need not be carried out switch motion, 200 off switch SW2 of LED driving circuit.
LED driving circuit 200 is in order to driven for emitting lights diode 204, and LED driving circuit 200 can be divided into booster type DC-DC transducer 230 and load 220 two parts thereof.Load 220 comprises the light-emitting diode 204 and current mirror 203 of serial arrangement, and this current mirror 203 couples light-emitting diode 204.When dimming control signal DCS2 enabled, 203 of current mirrors provided the drive current light-emitting diode 204 of flowing through.When dimming control signal DCS2 was forbidden, 203 of current mirrors ended drive current.Booster type DC-DC transducer 230 comprises control circuit 210, switch SW 2, inductance L 2, diode D2, capacitor C 2 and resistance R 21, R22.Control circuit 210 comprises PDM keyer 201 and signal controller 202.PDM keyer 201 is in order to provide pulse-width signal PS2.When dimming control signal DCS2 is forbidden, 202 off switch SW2 of signal controller.When dimming control signal DCS2 enabled, 202 pulse-width signal PS2 with PDM keyer 201 of signal controller passed to switch SW 2, use control switch SW2, and first end of switch SW 2 then outputting drive voltage Vout2 is given light-emitting diode 204.Thus, 202 of signal controllers can prevent the unnecessary switch motion of switch SW 2, and when light-emitting diode 204 need not be driven, but 202 off switch SW2 of signal controller use the minimizing power consumption.In the present embodiment, switch SW 2 is a power metal-oxide-semiconductor field effect transistor.
First termination of resistance R 21 is received driving voltage Vout2.First end of resistance R 22 couples second end of resistance R 21.Second end of resistance R 22 then receives earthed voltage.Resistance R 21, R22 constitute voltage detector.Voltage detector produces feedback signal FB2, in order to the state of indication driving voltage Vout2.PDM keyer 201 is according to the work period of feedback signal FB2 decision pulse-width signal PS2.
Other parts of boosting type converter 230 can be with reference to known boosting type converter 130.In other embodiments, buffer (not illustrating) can be coupled between signal controller 202 and the switch SW 2, uses the driving force that adds strong signal control 202.
Fig. 3 is the schematic diagram of a kind of LED driving circuit 300 of another embodiment of the present invention.The composition of LED driving circuit 300 and LED driving circuit 200 are similar, it should be noted that the function that PDM keyer 301 and signal controller 302 are increased.When feedback signal FB3 indicated the error condition of driving voltage Vout3,301 of PDM keyer were enabled rub-out signal FS.Feedback signal FB3 is provided by the voltage detector that R31 and R32 formed.In this embodiment, when driving voltage Vout3 is lower than preset threshold value, this error condition takes place then.For example, threshold value can be 90% of a maximum output voltage level.When rub-out signal FS enabled, even dimming control signal DCS3 forbidding, signal controller 302 still can be passed to switch SW 3 with the pulse-width signal PS3 of PDM keyer 301.When dimming control signal DCS3 was forbidden, 304 of light-emitting diodes can not be driven, and did not have the drive current light-emitting diode 304 of flowing through.Yet because driving voltage Vout3 keeps its electric charge for utilizing capacitor C 3, so driving voltage Vout3 may due to leakage current (Leakage) and little by little decline.In the present embodiment, when driving voltage Vout3 was lower than preset threshold value, the driving force of keeping driving voltage Vout3 was used in 302 operations that recover switch SW 3 of signal controller.
Fig. 4 is the schematic diagram of circuit of a kind of signal controller 302 of one embodiment of the invention.Signal controller 302 comprises or door 401 and and door 402.Or door 401 receives dimming control signal DCS3 and rub-out signal FS.With door 402 receive pulse-width signal PS3 with or the output signal of door 401.With the output signal SDS of door 402 in order to control switch SW3.Apparently, when one of them is enabled as rub-out signal FS and dimming control signal DCS3,302 of signal controllers pass to switch SW 3 with pulse-width signal PS3, and when rub-out signal FS and dimming control signal DCS3 are all forbidden, 302 off switch SW3 of signal controller.
Fig. 5 is the sequential chart of the signal of interest in the LED driving circuit 300, in order to show the standard operation situation of LED driving circuit 300.When time point T1, dimming control signal DCS3 is activated.Signal controller 302 is passed to switch SW 3 with pulse-width signal PS3.When time point T2, dimming control signal DCS3 forbidding.Signal controller 302 blocking-up pulse-width signal PS3 and off switch SW3.When time point T3, driving voltage Vout3 is lower than threshold value and rub-out signal FS enables.Therefore, signal controller 302 is passed to switch SW 3 with pulse-width signal PS3.When time point T4, dimming control signal DCS3 enables.Signal controller 302 still continues to transmit pulse-width signal PS3.When time point T5, driving voltage Vout3 is drawn high above threshold value, and error condition then disappears and rub-out signal FS forbidding.As long as dimming control signal DCS3 still keeps and enables, 302 of signal controllers continue pulse-width signal PS3 is passed to switch SW 3.When time point T6, dimming control signal DCS3 forbidding.Signal controller 302 blocking-up pulse-width signal PS3 and off switch SW3.
In sum, LED driving circuit comprises the operation of control circuit in order to the power controlling switch in the various embodiments described above.Control circuit comprises PDM keyer and signal controller.In the time need not keeping driving voltage, control circuit then cuts out power switch.Therefore the various embodiments described above have following advantage, low power consumption, high-effect, prevent that electric capacity from being overcharged and the ripple of driving voltage is less.The present invention is not restricted to LED driving circuit.For example, control circuit of the present invention can be applicable to any pulse-width modulation change-over circuit with load, uses and opens according to external signal or close.
Though the present invention with preferred embodiment openly as above; right its is not in order to qualification the present invention, those skilled in the art, without departing from the spirit and scope of the present invention; when can doing a little change and retouching, so protection scope of the present invention is as the criterion when looking the appended claims person of defining.